NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions


In which one of the following pairs the two items mean one and the same thing

  • Malleus - anvil

  • SA node - pacemaker

  • Leucocytes - lymphocytes

  • Haemophilia - blood cancer


SA node - pacemaker

The sinoatrial node (SA node), also known as sinus node, is a group of cells located in the wall of the right atrium of the heart. These cells have the ability to spontaneously produce an electrical impulse, that travels through the heart via the electrical conduction system causing it to contract. In a healthy heart, the SA node continuously produces action potential, setting the rhythm of the heart and so is known as the heart's natural pacemaker.


In a plant organ which is covered by periderm and in which the stomata are absent, some gaseous exchange still takes place through

  • aerenchyma

  • trichornes

  • pneumatophores

  • lenticels.



Due to continued formation of secondary tissues in the older stem and roots however the epidermis gets stressed and ultimately tends to rupture and followed by death of epidermal cells and outer tissues, and a new protective layer is developed called periderm. Structurally it consists of three parts Phellogen or Cork cambium, phellem or cork and phelloderm. Usually in the periderm of most plants, certain areas with loosely arranged cells have been found, which possess more or less raised and corky spots where the underneath tissues break through the epidermis. Such areas are universally found in the stems of woody plants. These broken areas are called lenticels, which perform the function of exchange of gases in the absence of stomata.


The bacteria Pseudomonas aeruginosa is useful because of its ability to

  • transfer genes from one plant to another

  • decompose a variety of organic compounds

  • fix atmospheric nitrogen in the soil

  • produce a wide variety of antibiotics


decompose a variety of organic compounds

Pseudomonas aeruginosa is a Gram-negative, aerobic rod belonging to the bacterial family Pseudomonadaceae. These bacteria are common inhabitants of soil water. They occur regularly on the surfaces of plants and occassionally on the surfaces of animals.

• The bacterium will grow in the absence of O2 if NO2 is available as a respiratory electron acceptor.
• They possesses the metabolic versatility. Organic growth factors are not required, and it can use more than thirty organic compounds for growth. Pseudomonas aeruginosa is often observed growing in "distilled water" which is evidence of its minimal nutritional requirements.
• It is able to grow at temperatures as high as 42 degrees.
• Its tolerance to a wide variety of physical conditions, including temperature, contributes to its ecological success and makes it suitable for decomposing a variety of organic compounds in varied environmental conditions.


Pruning of plants promotes branching because the axillary buds get sensitized to

  • ethylene

  • gibberellin

  • cytokinin

  • indole acetic acid.


indole acetic acid.

“It has been known since the 1930s that the plant hormone auxin is released by the plant’s actively growing tip and is transported down the main stem where it has an indirect effect on buds to inhibit branching. There are a number of ways in which the hormone exerts this effect and we have discovered a new path by which it works.”

The research suggests that for a shoot tip to be active, it must be able to export auxin into the main stem. But if substantial amounts of auxin already exist in the main stem, export from an additional shoot tip cannot be established


The total number of nitrogenous bases in human genome is estimated to be about

  • 3.5 million

  • 35 thousand

  • 35 million

  • 3.1 billion.


3.1 billion.

Genome size is usually stated as the total number of base pairs; the human genome contains roughly 3 billion base pairs.


Unidirectional transmission of a nerve impulse through nerve fibre is due to the fact that

  • nerve fibre is insulated by a medullary sheath

  • sodium pump starts operating only at the cyton and then continues into the nerve fibre

  • neurotransmitters are released by dendrites and not by axon endings

  • neurotransmitters are released by the axon endings and not by dendrites.


neurotransmitters are released by the axon endings and not by dendrites.

Neurotransmitters are molecules that fit like a lock and key into a specific receptor. The receptor is located on the next cell in the line. Therefore, nerve impulses cannot travel in the opposite direction, because nerve cells only have neurotransmitter storage vesicles going one way, and receptors in one place.


In Ulothrix meiosis takes place in

  • cells of the filament

  • holdfast

  • zygote

  • zoospores.



In Ulothrix sexual reproduction is of isogamous type. Two isogametes of + and - strain come together and fuse as a result a quadriflagellate zygospore is formed which floats on water after sometime it rests on the bottom of the pond at this time its four flagella disintegrate and a wall is formed surrounding it from all sides. After taking rest for a long period this zygote divides meiotically and gives rise to 16 zoospores. These zoospores come out of sac and give rise to the new plants of Ulothrix.


The sugarcane plant has

  • dumb-bell shaped guard cells

  • pentamerous flowers

  • reticulate venation

  • capsular fruits.


dumb-bell shaped guard cells

Guard cells are semilunar or kidney shaped cells which surrounds the minute apertures of epidermis called stomata. Guard cells are living and have chloroplast. In sugarcane and in some other monocots like doob, maize guard cells are dumb bell shaped.


Which one of the following categories of organisms do not evolve oxygen during photosynthesis

  • Red algae

  • Photosynthetic bacteria

  • C4 plants with Kranz anatomy

  • Blue green algae


Photosynthetic bacteria

Anoxygenic photosynthetic bacteria consume carbon dioxide but do not release oxygen. These include Green and Purple bacteria as well as Filamentous Anoxygenic Phototrophs (FAPs), Phototrophic Acidobacteria, and Phototrophic Heliobacteria.

Instead of using water to photosynthesize, like plants and cyanobacteria, purple sulfur bacteria use hydrogen sulfide as their reducing agent, which is why they give off sulfur rather than oxygen.


Which one feature is common to leech, cockroach and scorpion

  • Nephridia

  • Cephalisation

  • Ventral nerve cord

  • Antenna


Ventral nerve cord

Ventral nerve chord is the characteristic of lower chordates like leech, cockroach and scorpion